The research seeks to isolate, purify, and reconstitute the transport systems which mediate the translocation of organic anions, such as p-aminohippurate (PAH), across the surface membranes of renal proximal tubule epithelia. Isolated luminal (brush border) and contra-luminal (basal-lateral) membranes will be prepared from rabbit renal cortex. Experiments designed to detect phenomena such as saturability, competitive exchange diffusion, and competitive inhibition of PAH transport by probenecid and penicillin will be performed to establish the presence of a transporter which is specific for PAH. Evidence for co-transport of PAH with Na ion, H ion, or K ion will be sought, and the ability of an electrochemical gradient of these ions to drive PAH transport will be ascertained. If this ability exists, the contributions of a specific chemical gradient and of a non-specific electrical gradient to this driving force will be quantitated. Analysis of unidirectional flux will be used to determine kinetic parameters for the identified transport systems. All the experiments noted above will be performed with both luminal and contra-luminal membranes. After the transport systems of the luminal and contra-luminal membranes are characterized, the components of these membranes which effect transport of PAH will be purified and the transport system will be reconstituted in liposomes. The reconstituted system will be identified by its ability to transport PAH with characteristics qualitatively similar to those observed in native membranes. The ability of specific lipids to reconstitute transport will be assessed. By measuring transport rates over a temperature range that spans the transition temperature of the liposomal membrane, one may be able to differentiate a mobile carrier from a fixed channel as the agent of PAH's translocation. Some molecular characteristics of the purified transporting protein will be determined by gel electrophoresis.